Grid-tie solar PV in the United Kingdom

Started by sheddi, June 08, 2021, 06:11:49 AM

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sheddi

Yes, I *know* this is the off-grid living forum but I thought I would share my experiences of living on the grid (being part of the grid, even) with a grid-tied solar power system.

In January 2012, Mrs Sheddi received a small but unexpected windfall (an inheritance from an uncle). We decided to spend it on having a grid-tie solar PV system installed. We'd have liked 4kWp of panels, but at that time solar panel efficiency was around 14% and so we didn't have enough south-facing roof area. We settled for 2.72kWp - eleven 247Wp Samsung panels in a single string developing roughly 8 Amps at 330 Volts.


The panels were connected to a 2.5kW Kaco Powador inverter (a German brand but probably Chinese made). It's in our loft space and still I don't have a decent photo, but it looks like this.


The inverter output connects via our generation meter and a 16A dual-pole isolator to our domestic distribution board. power we use is takn directly from there, but any surplus power is exported to the grid. It was normal at that time (2012) for small-scale solar PV generators in the UK to have no export meter, so there is no record of how much of our generated power we use vs. exporting.


Our roof faces a little West of South, so the alignment is good but not the best. We don't get much generation before 1000 and the best period is from 1200-1500. In the summer, generation continues until after 2000 and as late as 2100 near the solstice. At the other end of the year, the sun has set by 1600. There's no significant shading (the closest trees and buildings are far enough away not to be a problem) but, as mentioned, we're in England which is hardly an ideal solar power location - we're at 51 degrees North, roughly the same as Calgary: https://en.wikipedia.org/wiki/51st_parallel_north

The system went live in late January 2012, and (at time of writing this in June 2021) we've generated 24000 kWh. The installers provided us with an illustrative calculation suggesting that in an "average" year we might expect to generate 2400 kWh, and over the past nine years we've exceeded that slightly.

So far, so good. How do the economics shape up? Well, the installation cost us £8350 (call it $13k) in £2012 money, which isn't trivial. Prices for PV systems have come down significantly since January and an equivalent system installed today would only cost ~£6000 (call it $10k). However by choosing to install in January we qualified for a significant UK government subsidy via a feed-in tariff, which (together with the savings on our power bills) means each kWh we generate is worth ~£0.50 / $0.80 to us for the next 25 years (and this return increases in line with inflation). We're thus expecting to gain ~£1200 of benefit annually, and the system will pay for itself in 7 years after which point we're in credit for the next 18 years. In purely financial terms, and even factoring in our natural gas use, our net energy bills for the next 25 years should be paid for.

Clearly, being a grid-tie system, we've not gained any significant degree of energy independence, but having the panels on the roof gives me options that I wouldn't have without them!

sheddi

Here's a chart from 2012 showing monthly output (red bars) vs the installers predicted output (blue bars), in kWh, up to the end of November.



January was a short month; the system wasn't commissioned until the month was more than half over.

There's an EU-run website here that gives estimates for the solar potential of the whole world, if you want to know what the potential is on your own patch of it:
http://re.jrc.ec.europa.eu/pvgis/index.htm

sheddi

How has it been since 2012? Pretty good, really. The system has required essentially no maintenance (I think I washed the panels once, using a the same water-fed brush I use for window cleaning) and the original inverter is still going strong. The inverter is likely to require replacing at some time but it's the only "active" piece of the system.

Economically, we're received subsidy payments of £12650 over that period. The install cost in 2012 was £8350 which, if you adjust for inflation, would be £10083 today (per this link) so we've more than broken even. The next eleven years of payments will be straight profit. We've also "saved" paying for somewhere between 8000 and 16000 kWh of electricity, which is in itself worth something - from roughly £800 to £2400, depending on exactly how much we've used and what we would have paid for it at that time.

Solar PV prices have fallen hugely since 2012 and an equivalent system, installed today, would be around £3000 - but they've stopped the subsidy scheme, so there's very little money to be made (there are a couple of options to offset costs but break-even typically takes 10 years). Also panel efficiencies have improved from ~14% to ~21% so we could fit 50% more watts into the same space - so replacing all the panels would get us to the 4kWp that we wanted in the first place!

If I wanted to make my system more resilient I'd swap the current inverter for a hybrid one (one where the inverter can charge batteries, or take battery power to produce AC) and add ~12 kWh of batteries. That would set me back around £3k to £4k so I'm not currently giving it serious consideration; I've got a 3kVA Honda-powered generator that got us through the only significant power outage in the past nine years without problems. If outages become more frequent (or I decide to switch to a wholesale pricing electricity tariff) I might reconsider.

sheddi

#3
I mostly left the system alone for nine years but, this year, I wondered about expanding it. I found a local vendor selling used 245-watt panels (taken, he claimed, from a solar farm that was upgrading - that 14% to 21% increase in efficiency again) for £63 (US$88) per panel, about £0.26 (US$0.33) per watt, which seemed a pretty good price; for comparison new panels are around £0.32/watt here currently but S&H makes small orders more expensive whereas I could collect the used ones myself. I bought four and screwed them to a frame I knocked together from 3"x2" pressure-treated lumber:


Sorry about the wonky photo, I had to hold my phone overhead to get a decent angle on things.

They are connected as a single string to a Growatt 1kW inverter:



The inverter is currently pegged into the ground just behind the panels (I should have bought some 12' lengths but had to make do with what Ihad, so apologies for the awful joinery):



Is it working? Yes, it is. The array is currently moveable which lets me do some experimentation. It makes most power facing south, but with it pointing east (as in the photo) it catches the sun earlier in the day than my roof-mounted array does and gives me 500 watts from about 0800 (daylight saving time), while the sun hasn't got over the ridge of my roof to illuminate the main array. Being down on the ground, it doesn't generate for as much of the day as my roof does so it might benefit me more facing east even if the total output is less.

As a DIY-installed, second-hand array it's not eligible for any payments at all, so economically it's not a great purchase b ut it does make me feel greener.

One benefit I do get from the extra panels is that my peak output is now above 3kW, not below it. This lets me run my 3kW electric water heater in the middle of sunny days for free, rather than relying on natural gas water heating. This is a (small) financial saving and a reduction in my household carbon footprint.

Halfapint

Very cool! I wish I got enough sun to justify it. Around her we can get the 240w panels for cheap. I think the last time I saw them they were 50$. I hear people drive down to California and load up trucks with the ones for the power companies are selling.
The original Half gettin sum land thread
https://www.zombiehunters.org/forum/viewtopic.php?f=39&t=111413

Quote from: SpazzyTell ya what... If Zombies attack and the world ends I'll hook tandem toddlers to a plow if it means I'll be able to eat...

Micon

Without that hybrid inverter, if your area loses grid power, your solar shuts off, right?  I bought a house that had a solar system already so I just accepted my free windfall, and didn't look much into it.  It was part of the overall cost so hey, free energy!  Now that I have researched more I understand that most systems in the US have a mandatory cut off when power goes out.  It makes sense from a safety perspective.  The idea is that if a line is down and power out on the grid, they dont want these systems feeding energy into them and charging the system that the repair people believe is dead.  Saves lives of the workers and all that, cant disagree.

It just makes me feel like its a completely wasted 'prep' concept though, and I am thinking the same thoughts as you - do I do "whatever" it is to make it so it charges something in the house if the grid is down, or do I just get a smaller 2ndary system for those times?  I've looked at the Tesla house batteries and I think with those it would do what I want, but as you pointed out, for many many thousands of dollars!

sheddi

#6
That's a very timely question, Micon, it's almost like you read my mind. Yes, UK grid-tie systems are also required to shut down in the event of grid failure. There are a couple of ways around it and I'm working towards one of them.

A couple of months ago I bought a used AC-coupled battery inverter to add to the system. Currently it's hanging from my wall waiting to be wired in. It's a Sofar ME3000 SP, one of these:
https://www.triplesolar.co.uk/sofar-me3000sp-solar-storage.html
I've also bought a set of sixteen LiFePO4 cells like this:
https://www.aliexpress.com/item/4000922994111.html
And a 16S battery management system like this:
https://www.aliexpress.com/item/1005001803913333.html

I'm currently waiting for some more components to arrive in the mail before I can get much further.

The intention is to put them all together and gain in two ways:

  • It will let me make better use of my solar electricity. In the daytime when the sun is shining the Sofar inverter will charge the battery and I can then use that power when thw sun isn't shining or if I need more power in the daytime than the panels are providing at that moment in time
  • The Sofar inverter has a UPS output. In the event of grid failure this is energised and the Sofar inverter will provide AC power to connected circuits until the battery goes flat.
The particular LiFePO4 cells I bought are quite small (only 25Ah) and the 48 volt pack they get built into will only hold 1kWh. If this works well as a proof of principle, I hope to increase to 100-200Ah of cells and boost the capacity to 5-10kWh.

What this doesn't let me do, in itself, is go fully off-grid. That would need a bit more work and possibly another box of electronics hanging on my wall.

QuoteI bought a house that had a solar system already so I just accepted my free windfall, and didn't look much into it.  It was part of the overall cost so hey, free energy!
Are you in one of the states that has net metering? (Do all the states have net metering?) If so you're in a better position financially than people installing new grid-tied solar PV in the UK currently are. The tariffs for selling power to the grid are roughly 1/3rd the price that you would have to pay to but it from the grid. This is why it makes (limited) financial sense to store the power my system generates rather than export it (the first item in my list of benefits).

Micon

Again I am woefully uninformed on what we do, cause I just saw it reduced my bill some, and was happy with that!  I dont think we do net metering here as I read that from a quick google.  What happens is 100% of my energy generated is sent to the grid.  The house is powered 100% from the grid.  So if Im generating 1kw and using 1 an hour in the middle of the day, it still shows I pull down 1 kw from the grid.  Basically the end of the month bill is a true-up that says "used 200, generated 120, charge for 80".  I have never had a month where I generated more than I used so I don't even know what happens with that case. 

We also have a bizzare incentive system called SRECs https://news.energysage.com/srecs-complete-overview/  From my understanding of that, it turns the power you generate into 'credits' that can be bought and sold, so that states (and businesses?) can claim they are green.  So if a place says 50% of their power is from renewable sources, they can just buy these SRECs which are tokens that say some energy was generated with solar'.  Even if that company didnt generate it, the buy the 'credit' for what I make.  Weird, but I get it.  Some states those are worth a LOT.  Mine not so much.

As far as what you are doing, I very much want to do something like that, but we are hyper regulated here, so I would end up needing to pay an electrician to do most of the work, or risk being out of luck (insurance wise) if there ever was a problem.  We are very DIY friendly here, until it comes to legality, lawsuits, and insurance!

sheddi

Quote from: sheddi on June 20, 2021, 10:00:18 AM
I've also bought a set of sixteen LiFePO4 cells like this:
https://www.aliexpress.com/item/4000922994111.html
And a 16S battery management system like this:
https://www.aliexpress.com/item/1005001803913333.html

I'm currently waiting for some more components to arrive in the mail before I can get much further.
If anyone is wondering what I'm planning to do with these, this YouTube video (not mine) takes exactly the same cells and a similar BMS and puts them together into a 48v battery:


https://www.youtube.com/watch?v=X_ucHHnh4Ik

Halfapint

Very cool Sheddi! Look forward to see what your poof of concept does.

Please excuse my ignorance, but say power goes down and it's the middle of the day. Your solar set up obviously stops sending power to the grid for safety reasons (similar to me shutting my main power switch when I start the genset). What happens to the power that those panels are producing? Just get sent to the earth/ground?

Is there a way to isolate the panels in your set up to first charge your batteries then any excess be sent to the grid?
The original Half gettin sum land thread
https://www.zombiehunters.org/forum/viewtopic.php?f=39&t=111413

Quote from: SpazzyTell ya what... If Zombies attack and the world ends I'll hook tandem toddlers to a plow if it means I'll be able to eat...

sheddi

#10
Quote from: Halfapint on June 30, 2021, 01:38:53 PM
Please excuse my ignorance, but say power goes down and it's the middle of the day. Your solar set up obviously stops sending power to the grid for safety reasons (similar to me shutting my main power switch when I start the genset). What happens to the power that those panels are producing? Just get sent to the earth/ground?

Yes, you're absolutely right, if the grid goes down (or my GFCI trips out, or anything else hapens to disconnect the panels from the grid) the inverter shuts down. Exactly what happens to the power is one of the things that takes a bit of getting your head around :D  and I'm sure @Blast could explain it better than I can. It's all to do with how a solar cell works.

A silocon solar cell is just a special piece of rock. If it was any other sort of rock the sun would shine on it and make it hot and that's all that would happpen, just like the clay tiles on my roof do. Because it's been carefully made to be a special rock the cell will convert some of that heat into electrical energy. If it's then connected through cables to the inverter and then to the grid, that energy will leave the cell as electricity and the cell will be slightly *less hot* than it would otherwise be. Once the electricity leaves the cell there's space in it for the cell to make more.

If for some reason the electricity can't flow, the cell won't be able to make any more and the energy will go back to being heat. The cell will get as hot as it would have done if it was just a rock.

QuoteIs there a way to isolate the panels in your set up to first charge your batteries then any excess be sent to the grid?

The Sofar inverter has a sensor - a directional current transformer - that clips onto the incoming grid supply. That sensor lets the transformer detect whether my house is importing power from the grid or exporting power to it.

The normal mode of operation works like this. If we're importing power from the grid, the Sofar will draw enough power from the battery and feed it into the system to balance the load (subject to its 3kW maximum inverter output and the capacity of my battery). If we're exporting, the Sofar will draw power from the system to balance the load and use it to charge the battery (subject to the maximum charge rate and battery capacity).

So yes, charging the battery will have priority over exporting to the grid.

I hope that all makes sense, in my head it does!

Halfapint

Yep! Makes perfect sense! I didn't know that about the PV cells, but yeah I guess that makes sense. And good to hear your system takes priority. Learning more about solar is on my list, but since it's not really feasible here, o just haven't done it.

Look forward to more posts!
The original Half gettin sum land thread
https://www.zombiehunters.org/forum/viewtopic.php?f=39&t=111413

Quote from: SpazzyTell ya what... If Zombies attack and the world ends I'll hook tandem toddlers to a plow if it means I'll be able to eat...

sheddi

#12
It works :)

My battery isn't quite as pretty as the one in the video but it's functional. Theee's currently more electrical tape involved than I really intended but until one of the missing parts orders arrives, it will suffice. And if I'm posting here about how my house mysteriously burned down, you'll have a clue as to why :D



My BMS - a Daly Smart BMS - includes a Bluetooth app so you can see what your battery is doing. Here's a screenshot:



(I know my cells are out of balance, I'll address that in due course.)

I now have just over a kilowatt-hour of grid-linked battery storage to play with. If it performs as hoped over the next couple of weeks I guess I will have to think about buying some more capacity to add to it.

sheddi

A week on and it still works, plus it hasn't burned my house down yet!


  • My solar panels charge the battery (indirectly) by sundown. They are currently producing more power than I can easily use in a day and the battery is usually full by 11am.
  • In the early evening when we're all awake and using electrical appliances (lights, laptops, Xbox and so on) we're using about 3-400 watts so the 1.2kWh in the battery lasts 3-4 hours.
  • An unexpected benefit (well, not exactly unexpected but it's proving more effective than I imagined) is that the battery helps during the daytime when I draw more power than the panels are generating. Eg. if I've got 2kW of solar but a 3kW load, the extra kW comes from the battery not the grid. I washed 2 loads of laundry today and, even though sunshine was patchy, used less than one kWh from the grid throughout the process.

I've got a bug in the settings I need to shake out; the inverter has been deciding to charge the battery in the middle of the night (usually between 2am and 4am), pulling needlessly from the grid. I've gone through the settings again today and will know tomorrow if I've fixed it. If not, I'll be back in the menus tomorrow.

All told I'm happy with it and have ordered another 60Ah / 3kWh of batteries to add in September/October when they arrive on a slow boat from China. (I'm not yet convinced that I use enough power in the summer, or generate enough in the winter, to justify more than 4kWh of battery storage.)

Financially the current system has a pretty long payback. I spent around £700 and am saving maybe £0.20 a day from increasing my self-consumption of solar electricity; at that rate payback will take 3500 days, call it 10 years. A lot of the cost was in the inverter which was necessary for any size system. The extra batteries will increase the cost to £1000 but I might then save £0.60 a day, so payback will be reduced to 1700 days, call it 5 years.

Plus, of course, I have 1.2kWh (to be 4.2kWh) of stored power in case of service interruptions, blackouts or whatever. The inverter has an emergency power supply function (not quite a UPS, there's a changeover time of "< 3 s") that I plan to add an outlet to in the near future.

Asparagus

This is an interesting system to see, as it's similar to what I'd like to do once I get a house. I have yet to see any companies building grid tied systems with batteries up here, but i really struggle to see the sense in not adding at least a small battery bank when investing so much money in solar in the first place.

That said, I'm up in Norway so solar in winter is a serious challenge: In the coldest months we have less than 2 hours a day of sunlight, with maybe 6 hours of daylight. Since I'm looking to buy a small farm I'll hopefully have a big barn roof to put a lot of panels on, but hopefully I'll find a place where I can combine with wind or hydro to take the load in winter. Solar is getting surprisingly popular up here thought, despite not doing much for half the year.

What do you use for heating and cooking? I'm guessing gas of some sort?

sheddi

#15
I can see that northern Norway could be a difficult place for solar power in the winter! If you drop a pin on the PVGIS map at https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP it will give you a reasonable estimate of how much power you can expect to generate in that location, month by month.

A quick look at Tromsø and I get nothing, zero, in December or January!

Yes, space heating, hot water and cooking are all by natural gas. I do have a back-up electric water heater which also gets used to top up the tank during settled weather when there's a steady surplus of solar electricity.

Asparagus

I'm not quite as far north as Tromsø, so i do at least get something... In my current house I consume as little as 200kwh in summer but up to 1000kwh in winter (I heat mostly with wood). According to that calculator a 10kwp solar system would produce 21kwh in December in my location, meaning I'd need a 500kwp system to cover my own consumption in winter... So that's not going to happen. Not much wind here either, but that might be viable in Tromsø as that region has much more wind most of the winter season.

I'll probably have to start by trying to reduce electricity demand in winter, and see what I'm left with. Most Norwegian homes are heated with some sort of electric heat or heat pump, water heating is electric, and cooking is about 98% electric. Some houses still have oil heating, but most of that is gone as fossil heating fuel was outlawed a few years ago (and anyone selling any sort of heaters advertised with "oil heaters are illegal" and conveniently forgot to mention that bio heating oil is available everywhere and require no investment (rant over, sorry). For my future small farmhouse i will hopefully be able to go all wood heat (with wood cut by me in my own forest) and have been researching gas stoves for cooking. That leaves water heating, which could be reduced with a heating coil in the main fireplace (I've tried to research that too, but there is little useful information except these systems exist and are common in Denmark). Maybe an on demand propane water heater? Time will show what i end up with.

sheddi

Your plans for your future house sound very interesting!

When you're ready to do so, should start your own thread where you will get more engagement from the forum members :)

Asparagus

Thanks, we'll see how things goes. I have the financing in order so I'm currently waiting for the right place to come up fore sale. The basic idea is to try and be as self-sufficient as possible, hopefully producing most of my own food with some excess for sale to cover my expences. Not sure how realistic that will be, time will tell... I'll probably start thread once i have bought a property, it might still be a year or two before the right one shows up.

sheddi

Quote from: sheddi on August 15, 2021, 04:39:49 PM
All told I'm happy with it and have ordered another 60Ah / 3kWh of batteries to add in September/October when they arrive on a slow boat from China. (I'm not yet convinced that I use enough power in the summer, or generate enough in the winter, to justify more than 4kWh of battery storage.)

The 60Ah cells arrived yesterday! They need balancing which is going to take a couple of days of careful attention but with a bit of luck they'll be in operation by early next week. (I have a suspicion that they're not really 60Ah, more like 50Ah. We'll see.)

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